Why did Claude Bernard consider vivisection necessary for physiological research?

Claude Bernard, a foundational figure in experimental medicine, argued that vivisection was indispensable for physiological research because he believed that medicine must be founded on experimental physiology to progress.1

In his seminal work, An Introduction to the Study of Experimental Medicine, Bernard maintained that the processes of life are mechanistically determined by physico-chemical forces. He asserted that experimenting on animals was an ethical necessity due to the potential for significant medical advancements and the extension of human life. By observing these processes in living organisms, Bernard sought to move beyond the vitalism of earlier physiologists and establish a rigorous, evidence-based approach to understanding the body's internal environment, or milieu intérieur.123